The invention relates to a method of cleaning a processing chamber to remove deposits which have accumulated on interior surfaces of the apparatus. For example, the method can be used to clean interior surfaces of a plasma enhanced chemical vapor deposition (PECVD) chamber in which films such as amorphous silicon, silicon oxide (SixOyHz), silicon nitride (SixNyHz), fluorinated silicon oxide (SiOxFy) or silicon oxynitride (SiOxNyHz) can be grown on a substrate. In particular, the invention relates to plasma cleaning to remove deposits on electrodes, interior walls, gas injection apparatus, and/or other components located within a PECVD process chamber.
It is conventional in the formation of semiconductor devices to deposit a variety of films on a substrate by plasma enhanced chemical vapor deposition. Examples of PECVD deposited films include amorphous silicon, silicon oxide (SixOyHz), silicon nitride (SixNyHz) and silicon oxynitride (SiOxNyHz). Such processes are effective at minimizing dopant diffusion effects in the treated devices as a result of the relatively low processing temperatures required. However, the PECVD process results in deposits building up on interior surfaces inside the plasma treatment chamber. The surfaces that the deposits adhere to can include electrode surfaces, walls of the plasma treatment chamber, clamping surfaces, gas injection apparatus and any other item that the plasma comes in contact with.
These deposits on the chamber interior surfaces adversely impact both device yield and apparatus production capability. Without cleaning, the deposits can accumulate to the point at which they tend to flake off from the interior surfaces onto the substrates being processed. Also, film thickness uniformity and deposition rate can be affected by these deposits. As such, the presence of deposits on the chamber interior surfaces is undesirable. To minimize these adverse effects, the interior surfaces of PECVD chambers are periodically cleaned. However, cleaning necessarily results in equipment downtime, which can be extremely costly from a production standpoint. To mitigate these problems, various in-situ chamber cleaning processes have been described.
For instance, U.S. Pat. No. 5,454,903 discloses an in-situ plasma cleaning method for a CVD or etch reactor. The plasma is generated by RF excitation using capacitively coupled parallel plate electrodes and/or an RF antenna surrounding the reaction chamber along the length thereof. The cleaning gas comprises C2F6, which can be supplemented by the addition of NF3 and He. U.S. Pat. No. 4,960,488 discloses a reactor self-cleaning process according to which a plasma is generated with RF parallel plate electrodes. A first, higher pressure gas cleaning step using fluorocarbon and oxygen gases is followed by a second, lower pressure cleaning step using a fluorinated gas, such as NF3. Similarly, U.S. Pat. No. 5,158,644 discloses a reactor self-cleaning process wherein a plasma is generated by parallel plate electrodes. This method requires a first, lower pressure plasma cleaning step followed by a second, higher pressure cleaning step, and is based on fluorocarbon/O2 chemistry.
U.S. Pat. No. 5,207,836 discloses plasma cleaning of an LPCVD chamber used in depositing tungsten or tungsten silicide films. The plasma is generated by a two electrode structure consisting of a grounded base/susceptor and showerhead. The cleaning gas is a fluorine based gas, such as SF6, CF4, C2F6 and NF3.
U.S. Pat. No. 5,356,478 describes a plasma cleaning method for removing carbon, organic residues, metals, metal oxides, and aluminum-containing residues from a plasma etching chamber, which includes forming a plasma from a cleaning gas mixture comprising oxygen and a chlorine containing gas and an optional fluorine-based gas. U.S. Pat. No. 5,011,705 discloses a chamber self-cleaning method, wherein a plasma is generated by microwave electron cyclotron resonance (ECR) or parallel plate electrodes. A cleaning gas, such as NF3 can be used in this process.
U.S. Pat. No. 4,786,352 describes a method of removing silicon oxide in a low pressure chemical vapor deposition (LPCVD) chamber using a cleaning gas which is decomposed to create etchant species in a plasma. Various electrode structures which extend along the length of a quartz processing chamber are used to generate the plasma. The cleaning gases include CF4, CF4+O2, C2F6, SF6 or NF3. Other cleaning gases include CF3Cl, CF3Br, Ccl4, Bcl3, Cl2, Hcl, O2 and combinations with or without inert gases.
U.S. Pat. No. 4,576,698 discloses a plasma cleaning method in low pressure LPCVD systems. According to this method, a plasma is generated between an anode and a cathode, wherein the anode is inserted along the central axis of the LPCVD reaction tube and the cathode is external to and surrounds the tube. The cleaning gas used is, e.g., P.D. 100. U.S. Pat. No. 4,749,440 discloses a method of cleaning oxide deposits on quartz boats. U.S. Pat. No. 4,816,113 discloses a process of removing carbon deposits inside a chamber with a plasma generated by microwave ECR. Use of oxygen or an oxygen-containing gas instead of a fluorine or chlorine compound gas is disclosed.
Various techniques for cleaning plasma reaction chambers are disclosed in commonly owned U.S. Pat. No. 5,356,478; in U.S. Pat. Nos. 4,657,616; 4,786,352; 4,816,113; 4,842,683, 4,857,139; 5,006,192; 5,129,958; 5,158,644 and 5,207,836 and Japanese Laid-Open Patent Publication Nos. 57-201016; 61-250185, 62-214175, 63-267430 and 3-62520.
In view of the state of the art, there still exists a need for an in-situ reactor cleaning process which can be carried out at high rates, and which can effectively remove deposits on interior surfaces of PECVD reaction chambers, which deposits can adversely affect device performance and yield.
The invention provides a plasma cleaning method for removing deposits in a plasma process chamber wherein substrates are processed. For example, the plasma process chamber can form a portion of a PECVD reactor. The method includes introducing a cleaning gas comprising a fluorine-based gas into the chamber. A planar plasma is formed by exposing the cleaning gas to an inductive field generated by resonating a radio frequency current in a substantially planar coil. A plasma cleaning step is performed by contacting interior surfaces of the chamber with the plasma for a time sufficient to remove the deposits on the interior surfaces.
The plasma cleaning method according to the invention provides an in-situ method for removing deposits on interior surfaces of PECVD reaction chambers at high rates. As a result, product yield can be maintained while equipment downtime is effectively reduced. By using interferometry, the endpoint for the chamber cleaning can be determined.